Production of methylsemicarbazides and monomethylhydrazines



United States Patent 3,387,030 PRODUCTION OF METHYLSEMICARBAZIDES AND MONOMETHYLHYDRAZINES Charles R. Walter, Jr., Hopewell, Va., assignor to Allied Chemical Corporation, New York, N .Y., a corporation of New York No Drawing. Continuation-impart of application Ser. No. 104,222, Apr. 20, 1961. This application Oct. 23, 1961, Ser. No. 147,087

5 Claims. (Cl. 260-554) This is a continuation-in-part of my copending application Ser. No. 104,222 filed Apr. 20, 1961, and now abandoned. This invention relates to an improved process for the preparation of monomethylhydrazine from a nitrosomethylurea. More particularly, it relates to an improved process for the reduction of a nitrosomethylurea to its corresponding N-amino derivative.

The rapid increase of interest in guided missiles and rockets for military use has created a great demand for high energy fuels such as unsymmetrical dimethylhydrazine and monomethylhydrazine.

A process has been proposed for the preparation of monomethylhydrazine wherein N-methyl-N-nitrosourea is reduced in the presence of zinc and acetic acid to the corresponding N-amino compound which is subsequently hydrolyzed with aqueous mineral acid to the salt of monomethylhydrazine. The reduction step of this process, which uses the nascent hydrogen produced by the action of acid on zinc, is quite costly and corrosive to equipment.

In an attempt to circumvent the high cost and corrosiveness inherent in the chemical reduction of nitroso groups, a procedure has recently been proposed for the production of unsymmetrical dimethylhydrazine wherein the N- nitrosodimethylamine produced by the nitrosation of di methylamine is reduced by catalytic hydrogenation over a platium catalyst. Since a similar route to monomethylhydrazine is not open because of the instability of nitrosomethylamine, a different procedure is necessary for the preparation of monomethylhydrazine.

It is accordingly a principal object of the present invention to provide an improved, economical process for hydrogenating N-nitroso-Nmethylurea and N-nitroso-N, N'-dimethylurea to produce the corresponding N-amino derivatives which can be hydrolyzed to produce monomethylhydrazine.

Another object of the invention is to provide a process for hydrogenating N-nitroso-N-methylurea and N-nitroso- N,N'-dimethylurea to the corresponding amino derivatives which, in its preferred embodiment, avoids the high cost and corrosive nature of the prior art hydrogenation processes.

In accordance with the present invention, a nitrosomethylurea selected from the group consisting of N- nitroso-N-methylurea and N-nitroso-N,N-dimethylurea, is hydrogenated at superatmospheric pressures, and at temperatures within the range of 20 to 60 C., in the presence of a finely-divided, supported, platinum catalyst at a conoentration of about to about 125 grams of catalyst per mol of nitroso compound in a liquid reaction medium in which the nitroso compound is at least partly soluble. The corresponding N-amino compounds thus produced are hydrolyzed with aqueous mineral acid to the salt of monomethylhydrazine.

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The reactions involved in the process of this invention are represented 'by the following equations:

wherein R is either methyl or hydrogen.

The nitrosomethylurea and ntrosodimethylurea which are used as starting materials for the monomethylhydrazine syntheses may be readily obtained by condensing one or two moles of methylamine with urea under acidic conditions, and nitrosating the resulting N-methyl or N,N- dimethylureas. Alternatively, dimethylurea may also be prepared from the reaction of methylamine with phosgene.

The nitrosation may be eifected with sodium nitrite in the presence of an acid such as hydrochloric or nitric, and the nitrosomethylurea is readily recovered from the reaction mixture by filtration. The crude nitroso compound may be hydrogenated directly, or it may be subjected to a preliminary purification treatment such as recrystallization before hydrogenation. When N nitroso- N,N'-dimethylurea is hydrogenated within one to two days of its preparation from dimethylurea, higher yields of the N-amino derivative are obtained than when the material is used after prolonged storage under ordinary conditions.

The catalysts for the hydrogenation step are those platinum-supported catalysts which contain 2 to 15 percent by weight of platinum. Although an alumina support is preferred, other supports such as carbon, kieselguhr, pumice, and silica are applicable. Such platinum-supported catalysts may be produced by known procedures. For instance, a platinum salt such as platinic chloride may be deposited on alumina particles, treated with sodium hydroxide, and then reduced to form a platinum deposit on alumina.

The catalyst is mixed with a nitro-somethylure-a, in a liquid reaction medium, to form a slurry or suspension having a concentration of from 10 to 125, preferably 15 to 30, grams of catalyst per mole of nitrosomethylurea. The weight given includes the weight of the support. The proportion of the liquid phase is not very critical, but there should 'be sufficien-t liquid phase present to form a slurry or suspension of the other ingredients It is preferred to use a liquid reaction medium containing 2 to 40 weight percent of irit-rosomethylurea. A variety of solvents meet this solubility requirement. The most notable of these are water and the aliphatic monoand dihydric alcohols. Water is the prefenred reaction medium although solvents such as aqueous acetic acid, ethanol, ethylene glycol, and mixtures of these solvents function almost as well.

The hydrogenation is preferably carried out in an acidic reaction medium, and highly alkaline conditions are avoided, since alkalis, as is well known, tend to decompose the nitrosomethylureas. While the hydrogenation can be carried out successfully in highly acidic media, I prefer to use a reaction medium which is only mildly acidic, and which has an initial pH below 7 but not less than about 6 at the start of the reaction. Progression of conditions to a neutral pH of 7 or slightly above, toward the end of the hydrogenation may sometimes occur and does no harm. The preferred acidic reaction medium may be obtained in any desired mariner either by the use of an acid as a component of the reaction medium, or by utilizing a freshly prepared nitrosomethylurea which retains all or a portion of the acid used in its preparation, or by limiting the quantity of the somewhat alkaline catalyst (pH about 9.3) to an amount which leaves the reaction medium in an acid condition through the influence of the naturally acidic nitrosomethylurea, the pH value of nitrosomonomethylurea being in the neighborhood of about 4.6.

The hydrogenation may be carried out continuously Carrying out the hydrogenation under the preferred conditions, at pH values below 7 but not less than about 6, and using the preferred alumina supported platinum catalyst, I obtain high yields of monomethylhydrazine upon hydrolysis of the hydrogenation product; with such pH conditions and catalyst, yields of 65 to 75 percent or more are obtained in 2 to 4 hours at 25-45 C. under hydrogen pressures of 800 to 2000 p.s.i., as brought out in the specific examples which follow and which further illustrate the invention. In the examples, parts and percentages are by weight, and temperatures are in degrees centigrade. The nit-roso compounds used in these examples were prepared by nitrosation with sodium nitrite and nitric acid, and isolation of the nitroso comby introducing -a slurry of nitrosomethylurea and catalyst 15 pound by filtration.

into a reactor designed to give the proper residence time,

and withdrawing the reaction products from the exit of Examp 1 this reactor. Alternatively, the reaction may be carried out hatchwise Freshly prepared N-nitroso-N-methylurea (5 parts) In both cases, the amount of hydrogen introduced is 20 Was f' to Tshahfless steel YP autoclave in excess of the stoichiometric amount required for the along Wlth Water P and 200 h 5 P Q reduction. The amount of excess is not critical. Pt 2 3 0d'lalysl P T Teactlofl medllfm Although initial pressures of hydrogen of at least 50 Q Q Hydrogen was llltmduced provide p.s.i. are necessary for the hydrogenation of the nitroan lnlfila'l Pressure of 1425 P- The autwlave Was somethyqurea compounds to h comresponding i roclced at a temperature of about for about 2 hours derivatives, optimum yields are obtained when said hywhfch modes hydrogen Were absorbed P drogena-tion is conducted at initial pressures of hydrogen mole P compcund, and the Pressure pp to ranging from about 800 to 2000 p.s.i. The rate at which 1175 P- the hydrogenation proceeds, appears to be a function, The crude, aqueous product was filtered to isolate in part, of the pressure of the hydrogen. Consequently, 30 N-methyl-N- aminourea. This product was refluxed for higher hydrogen pressures should be conducive to greater 8 hours with 177 parts of aqueous 37% HCl, then made rates of hydrogenation to the extent that the maximum basic to a pH of l0-12 with 25% sodium hydroxide, pressure which may be use-d is limited primarily by ecoand distilled until the distillate no longer gave a positive nomic considerations. Fehlings test. The product was a dilute, aqueous solu- It must be pointed out, however, that it is desirable tion of 'monornethylhydrazline, which was isolated from to allow the pressure to. drop to about 1000 p.s.i. after the solution as the sulfateby the addition of 7 parts of the reaction has progressed to the point where approxi- 96% sulfuric acid, and evaporating the resulting solumately 50 percent of the nitros-omethylurea has been tion to dryness. Yield (percent of theoretical based on reduced to the N-amino compound. This decrease in nitrosomethylurea) was 66.4 percent. pressure is apparently necessary to avoid the formation 40 of byproducts produced by the interaction of reduced and Example 2 unreduced compounds.

Although a reaction temperature of 20 to 60 0. is Freshly p p y1 was .appiicabqe f the hydrlogenation process, the range f o hydrogenated in accordance with the procedure described 25 to C. is preferred. 45 in Example 1. Ii1 the hydrogenation step, 5 parts of cata- The hydrogenation time is dependent on the concen- Y was mlxed Wlth 150 Parts of i and parts of tration of nitrosomethylurea, catalyst concentration, ternmtmsomethgluref- The hyd1:o.gnat10n proceeded for perature, and pTeSSuTe' hours at 25 55 under an initial pressure of 1500 psi.

The monomethylhydmz-ine pmduct is readily Ohtaim No additonal hydrogen was added during the course of able by hydrolysis of the N-amino-N-methylurea derivathe hydrogenalflon' The hydrogen pressure was below hive produwd by the hydmgehation process discussed about 1000 pm. after hydrogen had been absorbed to the hereinahove N methy1 extent of one mole of hydrogen per mole of nitroso comcompound is hydro1yzed by fl i it in an pound. The total quantity of hydrogen absorbed amounted ous, mineral acid such as hydrochloric acid, sulfuric, or to moles p mo f mtroso compound. After hyphosphofic, at about Q :5 sevefaq hours The drolysis and separation as described in Example 1, the methylhydrazine salt thus prepared can be obtained as yield of monomethylhydl'azine was Percent based the free base by the addition of a water-soluble alkali. 0n the nitrosodimethylurea- The hydroxides of the alkali metals, e.g., sodium hy- Additional examples are provided in the data in Table droxide, are particularly useful. The monomethylhydrazine I. The hydrogenation catalyst in every case was 200 mesh can then be distilled in order to recover the pure product. (50 5 percent Pt on A1 0 TABLE I Percent Hydrogenation Percent Percent Nitroso Initial Yield, Example Catalyst compound Pressure, Temp., Time, methylin H20 in Hi0 p.s.i. 0. hrs. hydrazine 1 N-methyl-N-nitrosourea used.

2 Initial pH of reaction medium 6.8.

3 N,N-dimethyl-N-nltrosourea used.

4 Ethanol used as a solvent instead of water.

5 N,N-dimethyl-N-nitrosourea had been stored for two weeks prior to use.

While the above describes the preferred embodiments of the invention, it will be understood that departures may be made therefrom within the scope of the specification and claims.

I claim:

1. A process for the production of a derivative of urea having the formula wherein R is a member selected from the group consisting of hydrogen and methyl, which comprises hydrogenating a nitrosomethylurea compound selected from the group consisting of N-nitroso-N-methylurea and N-nitroso-N,N'- dimethylurea in intimate contact with an alumina supported platinum catalyst contained in an aqueous reaction medium having a pH value ranging from about 6.2 to 6.8 wherein the concentration of said supported catalyst is from about to 125 grams per mole of said nitrosomethylurea and wherein said hydrogenation occurs under a hydrogen pressure of from 50 p.s.i. to 2000 p.s.i., and at a temperature of from C. to 60 C.

2. A process as described in claim 1, wherein the platinum-alumina catalyst contains from about 2 to about 15 percent by Weight of platinum, and from about 85 to about 9-8 percent by weight of alumina.

3. A process as described in claim 1, wherein the aqueous solution of the nitrosomethylurea compound contains from about 2 to about 40 percent by weight of said nitrosomethylurea compound.

4. A process for the production of monomethylhydrazine which comprises hydrogenating a nitrosomethylurea n t CH3NC-NHR wherein R is a member selected from the group consist ing of hydrogen and methyl, and hydrolyzing said amino derivative with aqueous, mineral acid to isolate the salt of monomethylhydrazine.

5. A process as described in claim 4 wherein the mineral acid is a member selected from the group consisting of hydrochloric, sulfuric, and phosphoric acids.

References Cited UNITED STATES PATENTS 11/1960 Lum et al 260-554 OTHER REFERENCES Degering: An Outline of Nitrogen Compounds (1950) pp. 377-78.

HENRY R. JILES, Primary Examiner. 

4. A PROCESS FOR THE PRODUCTION OF MONOMETHYLHYDRAZINE WHICH COMPRISES HYDROGENATING A NITROSOMETHYLUREA COMPOUND SELECTED FROM THE GROUP CONSISTING OF N-NITROSO-N-METHYLUREA AND N-NITROSO-N,N''-DIMETHYLUREA MIXED WITH WATER IN THE PRESENCE OF AN ALUMINA-SUPPORTED, PLATINUM CATALYST IN A CONCENTRATION OF ABOUT 10 TO ABOUT 125 RAMS OF SAID CARALYST PER MOLE OF AID NITROSOMETHYLUREA UNDER A HYDROGEN PRESSURE OF ABOUT 50 P.S.I. TO ABOUT 2000 P.S.I., SAID HYDROGENATING MIXTURE HAVING A PH VALUE RANGING FROM ABOUT 6.2 TO 6.8 AND A TEMPERATURE OF ABOUT 20* TO ABOUT 60*C., RECOVERING FROM SAID HY DROGENATION REACTION MIXTURE AN N-AMINO DERIVATIVE OF THE GENERAL FORMULA 